struct ListNode* reverseList(struct ListNode* head)
{
 struct ListNode* n1=NULL;
 struct ListNode* n2=head;
 while(n2)
  {
	struct ListNode*n3=n2->next;
	n2->next=n1;
	n1=n2;
	n2=n3;
  }
  return n1;
}
